Burner unit for carbonaceous gas waste

ABSTRACT

A burner unit is disclosed which is particularly suitable for use with a furnace for burning carbonaceous waste gases. The air and fuel gas mixture for igniting the burner is mixed at the front end of the burner, to prevent &#39;&#39;&#39;&#39;flashback&#39;&#39;&#39;&#39; into the burner body. Mounted on the front end of the burner is a closure disc, which is connected into an air operator unit. The air operator unit moves the closure disc backward or forward in response to air pressure fluctuation in the mixing chamber. Moving the disc back and forth regulates the velocity of air which passes through an annular opening defined between the disc and the front end of the burner. Regulating the velocity of the air enables precise control of the firing rate of the burner.

United States Patent 1191 Giadney et al.

[ BURNER UNIT FOR CARBONACEOUS GAS WASTE [75] Inventors: Frank L.Gladney, Freeport;

Michael L. Turner, Lake Jackson, both of Tex.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: July 24, 1972 [21] Appl. No.: 274,217

1451 Oct. 9, 1973 3,486,834 12/1969 Frey et a1 431/12 PrimaryExaminer-Edward G. Favors Attorney-William M. Yates et al.

[57] ABSTRACT A burner unit is disclosed which is particularly suitablefor use with a furnace for burning carbonaceous waste gases. The air andfuel gas mixture for igniting the burner is mixed at the front end ofthe burner, to prevent flashback into the burner body. Mounted on thefront end of the burner is a closure disc, which 52 U.S. c1. 431/89,431/181 is connected into an air Operator unit- The air w [51] Int. Cl.F23n 1/02 tor unit moves the closure disc backward or forward 58 Fieldof Search 431/89, 12, 181 in response to air pressure fluctuation in themixing chamber. Moving the disc back and forth regulates the 5References Cited velocity of air which passes through an annular open-UNITED STATES PATENTS ing defined between the disc and the frontend ofthe 3 135 314 6/1964 Bummer 431,12 burner. Regulating the velocity ofthe air enables pre- 3,217,779 11/1965 Reed et al... 431/181 use controlthe finng rate of the burner 3,315,726 4/ 1967 Williams 431/89 3 Claims,2 Drawing Figures F Fue/ air 10 PATENTEU URI 9 I973 NQ C BURNER UNIT FORCARBONACEOUS GAS WASTE BACKGROUND OF THE INVENTION Various chemicalproducts, such as chlorinated solvents, are obtained by the chlorinationof methane or higher hydrocarbons. One of the waste products left overfrom the reaction process is a mixture of carbonaceous gases. Since itis undesirable to discharge the chlorinated gas waste into theatmosphere, it is usually disposed of by burning in a furnace with asealed combustion chamber.

Typical conventional burners which are used to ignite the waste gasmixture are units usually referred to as fixed flow" burners. The fixedflow burners, however, have certain drawbacks when employed in a furnacefor burning carbonaceous gas waste. One disadvantage is that the fuelmixture will usually pre-ignite within the body of the burner. Thisoccurrence, which is generally referred to as flashback, frequentlyresults in premature burnout of the burner body. Another drawback isthat the burner tip is constructed with a perforated screen insertedtherein, which is always open to the furnace combustion chamber. As thewaste mixture burns, therefore, it develops an extremely hightemperature and the resulting heat will back up through the screen intothe burner body.

SUMMARY OF THE INVENTION In the present burner unit, the chamber formixing the fuel gas and air has an open front end and a closed rear end.In use, the burner is mounted on a furnace with the front end incommunication with the combustion chamber of the furnace. A tube sheetis positioned cross-wise in the mixing chamber between the front andrear end. A front compartment is defined in the mixing chamber by thespace between the front end and the tube sheet. The space between thetube sheet and the rear end provides a rear compartment.

Positioned in the front compartment of the mixing chamber is a tubebundle, made up of several spaced apart, parallel open end tubes. Therear end of each tube fastens into the tube sheet, so that the open endcommunicates with the rear compartment. The opposite open end of eachtube is in communication with the front compartment. Fuel gas isconducted into the rear compartment through a fuel gas inlet conduit. Asimilar inlet conduit conducts air into the front compartment.

A pilot tube, open at both ends, is slidably mounted on the tube sheetand rear end of the mixing chamber. This tube, which extends centrallythrough the rear and front compartments of the mixing chamber, carries afuel-gas air mixture into the furnace for the pilot flame. Mounted onthe front end of the slidable pilot tube is a closure disc with acentral opening therein. The closure disc can be moved backward orforward, to close or open the front end of the mixing chamber, inresponse to air pressure fluctuation in the chamber.

Connected into the rear end of the pilot tube is a pilot fitting, withan inlet conduit for carrying a fuel gas-air mixture into the fitting.An ignitor fitting, which connects into the pilot fitting, includesseparate inlets for conducting air and fuel gas into the fitting. Theignitor fitting includes a means for igniting the fuel gas-air mixture.An ignitor tube is provided by a small tube, open at both ends, whichextends centrally through the pilot fitting and pilot tube. The rear endof the ignitor tube 2 connects into the ignitor fitting and the frontend is flush with the front end of the opening in the closure disc. Thepurpose of the ignitor tube is to carry the ignited fuel mixture fromthe ignitor fitting into the furnace combustion chamber.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view, partly insection, of one embodiment of the burner unit of this invention. In FIG.1 the burner unit is shown installed in a typical operating position inthe combustion chamber of a furnace.

FIG. 2 is a cross-section view, taken on line 22 of FIG. 1, lookingtoward the front end of the burner unit.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring particularly to FIG. Iof the drawing, the burner unit is indicated generally by numeral 10.The main part of burner 10 comprises a fuel mixing chamber 11, which hasan open front end 12 and is closed at the rear end by a cover plate 13.In a typical use, the burner 10 is mounted in the combustion chamber ofa furnace. As shown in FIG. 1 the burner 10 is mounted on a wall 14 ofthe furnace combustion chamber, with the open front end 12 being incommunication with the combustion chamber of the furnace.

A tube sheet 15 is positioned crosswise in mixing chamber 11 and it isspaced from each end of the chamber. Tube sheet 15 is held in place inmixing chamber 11 by being clamped between opposing flange members 16and 17 on chamber 11. A rear compartment 18 in mixing chamber 11 isdefined by the space between tube sheet 15 and cover plate 13. Also, afront compartment 19 is defined by the space between tube sheet 15 andthe front end 12 of chamber 11.

Positioned inside the mixing chamber 11 is a tube bundle. The tubebundle is made up of several open end tubes 20, which are positioned inspaced apart, parallel relation. Each tube 20 is connected at the rearend into tube sheet 15, so that one open end of each tube is incommunication with rear compartment 18. From tube sheet 15 the tubes 20extend lengthwise into the front compartment 19 of mixing chamber 11, so

that the opposite open end of each tube communicates with compartment19,

An inlet conduit 21 is connected into rear compartment 18 between flange16 and rear cover plate 13. Conduit 21 provides a means for conducting afuel gas into rear compartment 18. A second inlet conduit 22 isconnected into the front compartment 19 between flange l7 and a mountingflange 23, by which burner 10 is fastened to the furnace wall 14.Conduit 22 provides a means for conducting air into the frontcompartment 19.

Means for carrying a fuel gas-air mixture into the furnace combustionchamber, to initiate a pilot flame, is provided by a pilot tube 24,which is open at both ends. The pilot tube 24 is slidably mounted ontube sheet 15 and on rear cover plate 13, the tube being carried by thefront end opening 12 in mixing chamber 11. Con versely, by moving thepilot tube 24 forward, disc 26 will disengage from the front end opening12 in chamber 11. The rear end of pilot tube 24 is connected into onebranch of a cross fitting 27, which functions as a pilot fitting. A fuelgas-air mixture is directed into pilot fitting 27 through an inletconduit 28, which is connected into a second branch of fitting 27. Pilotfitting 27 also includes a thermocouple sensor 29, which is connectedinto a third branch of the fitting directly opposite to inlet conduit28.

Connected into the fourth branch of pilot fitting 27, which is oppositeto the pilot tube connection, is the front end of an ignitor fitting 30.Basically, the ignitor fitting 30 consists of a coupling which isthreaded on both ends, with a central lengthwise bore 31 therein, whichintersects a crosswire bore 32 near the rear end of the fitting. Aninlet conduit 33, which is connected into one end of bore 32, is fordirecting a fuel gas into the bore 31 in fitting 30. Connected into theopposite end of bore 32 is a second inlet conduit 34, through which airis directed into bore 31 of fitting 30. Means for igniting the fuelgas-air mixture in fitting 30 is provided by a spark plug 35, which ismounted in the fitting with the electrodes seated in bore 31. Anelectrical lead 36 connects the spark plug 35 into a source of power(not shown).

A small diameter, open end ignitor tube 37 provides means for carryingthe ignited fuel gas-air mixture from fitting 30 into the furnacecombustion chamber. The rear end of tube 37 is fitted into bore 31 offitting 30. From fitting 30 the tube 37 extends centrally through thepilot fitting 27 and pilot tube 24, with the front end being flush withthe front end of opening 26a in disc 26. The rear end of ignitor fitting30 is connected to a piston rod 38, which operates a diaphragm plate(not shown) inside an air operator unit 39. Piston rod 38 is slidablewithin a collar 40, which is mounted at the base of the air operatorunit 39.

Fastened to opposite sides of collar 40 are arm members 41 and 42, whichare attached to leg members 43 and 44. In the unit illustrated hereineach of the leg members 43 and 44 comprises two separate pieces of angleiron which are slidably connected. The leg members are slidablyconnected to permit back and forth movement of closure disc 26. The endof each leg member which is opposite to collar 40 is fastened to therear end of mixing chamber 11 adjacent to cover plate 13. The combinedstructure of arm members 41 and 42 and leg members 43 and 44 defines ayoke member for attaching the air operator unit 39 to mixing chamber 11.

A pneumatic multiplying relay 45 provides means for actuating the airoperator unit 39 in response to air pressure fluctuation in the frontcompartment 19 of mixing chamber 11. The air pressure fluctuation incompartment 19 is monitored by relay 45 through an air line 46, whichconnects the relay into air inlet conduit 22. The air pressure signalreceived by relay 45 is multiplied by the relay and sent through asecond air line 47 to another pneumatic relay (not shown) in airoperator unit 39. Regular instrument air required by the relay 45 isdirected into the instrument through a third air line 48.

In one example of the practice of this invention, the burner unit isused to ignite a waste product which comprises a mixture of carbonaceousgases. In carrying out the operation, the waste gas is first directedinto a furnace combustion chamber in which the burner unit 10 isinstalled. To initiate a starter flame, a mixture of fuel gas and air isdirected into bore 31 of ignitor fitting 30, through the fuel inletconduit 33 and air inlet conduit 34. Spark plug 35 is then fired toignite the fuel mixture and the flame is propagated through ignitor tube37, so that the flame burns at the front edge of opening 26a and closuredisc 26.

In the event the starter flame is not being propagated through ignitortube 37, the tube will not heat up. If the starter flame should go out,therefore, the thermocouple 29 will immediately sense the drop intemperature, so that corrective action can be taken. With regard toigniting the starter flame, this can be done by ignition means otherthan spark plug 35. For example, any device suitable for igniting a fuelgas mixture may be used. Also, as an alternative procedure, the starterflame can be ignited by positioning the ignitor device immediatelyadjacent to the front opening in ignitor tube 37. Once the starter flameis lit, a second fuel gasair mixture is directed into pilot fitting 27through inlet conduit 28. The resulting fuel mixture travels forwardthrough pilot tube 24, around ignitor tube 37, and is ignited by thestarter flame at the front edge of opening 26a. The second flame thenfunctions as a pilot flame.

After the pilot flame is lit, a charge of fuel gas is directed into therear compartment 18 of mixing chamber 1 1 through the fuel gas inletconduit 21. From compartment 18 the fuel gas travels through the tubes20 and spills out into the front compartment 19 of chamber 11immediately behind the closure disc 26. Simultaneously, a volume of airis directed into compartment 19 through air inlet conduit 22. As the airand fuel gas mix in compartment 19, the mixture is ignited by the pilotflame to initiate the burner flame. The burner flame, in turn, ignitesthe gaseous mixture in the furnace combustion chamber.

Once the burner flame is lit, the flame is sustained by closelycontrolling the firing rate of the burner. Specifically, the firing rateis controlled by regulating the velocity of the air which passes throughthe annular opening between the periphery of closure disc 26 and theinner wall surface of the open front end 12 of mixing chamber 11. Forexample, if the air velocity pouring through this annular opening shouldget too high, it will extinguish the burner flame, which is actuallyburning at the outside face of closure disc 26. In such a situation, therapidly increasing air velocity will build up a back pressure incompartment 19 of mixing chamber 11. To correct the situation, the airpressure is constantly monitored by multiplier relay 45 through air line46 into conduit 22. Once the air pressure in conduit 22 exceeds apredetermined level, therefore, which is set in relay 45, the air signalwill actuate the relay.

The relay 45, in turn, multiplies the air signal and sends it throughthe air line 47 into the air operator unit 39. In unit 39 the air signaltriggers a second relay, which operates a diaphragm assembly to pushpiston rod 38 forward. In its forward movement, the piston rod 38 pushesthe pilot tube 24 and closure disc 26 forward to increase the size ofthe annular opening at the front end of mixing chamber 11. Increasingthe size of the annular opening, therefore, reduces the air velocity toa level low enough to sustain the burner flame.

If a condition of no air pressure should occur in front compartment 19,during operation of burner 10, the air operator unit 39 will pull theclosure disc 26 backward to close off the front opening of the burnerfrom the furnace. Such a condition can occur, for example, if there is amalfunction in the air system, or if the burner is turned off. Inpractice, for example, the burner opening is usually closed off when theburner is not operating. This is done to protect the inner structure ofmixing chamber 11 from the furnace flame, so as to prolong the life ofthe burner.

One example of a fuel which may be used in the burner unit of thisinvention, is a mixture of air and methane gas. In general, asatisfactory burner flame is achieved by mixing the fuel and air inapproximately stoichiometric proportions. A particular advantage of thepresent burner over the fixed flow burners is that it can operate over awide range of heat release and throughput. in practice, the presentburner unit was operated at a maximum heat release of about 2.07 millionBtu/hr., which corresponds to a throughput of about 2,298 SCFl-l ofmethane and 21,905 SCFH of air. The minimum of heat release wasdetermined to be about 20,000 Btu/hr., which is equivalent to athroughput of about 22.2 SCFl-l of methane and 211 SCI-H of air.

What is claimed is: I

1. A burner unit for use with a furnace for burning combustible gases,which includes:

a. a fuel gas mixing chamber having an open front end and a closed rearend, the burner unit being adapted for mounting on a furnace with theopen front end of the mixing chamber in communication with thecombustion chamber of the furnace;

b. a tube sheet positioned crosswise in the mixing chamber and spacedfrom each end of the chamber;

c. a rear compartment in the mixing chamber defined by the space betweenthe tube sheet and the rear end of the chamber;

d. a front compartment in the mixing chamber defined by the spacebetween the tube sheet and the front end of the chamber;

e. a tube bundle comprising several open end tubes in spaced apart,parallel relation, each tube being connected at one end into the tubesheet, such that one open end of each tube communicates with the rearcompartment of the mixing chamber and the opposite open end of each tubecommunicates with the front compartment of said mixing chamber;

f. a fuel gas inlet conduit connected into the rear compartment of themixing chamber, which is adapted for conducting a fuel gas into saidrear compartment;

g. an air inlet conduit connected into the front compartment of themixing chamber, which is adapted for conducting air into said frontcompartment;

h. a pilot tube which has an open front end and an open rear end, whichis slidably mounted on the tube sheet and the rear end of the mixingchamber, which extends centrally through the rear compartment and thefront compartment of the mixing chamber, and which is adapted forconducting a fuel gas-air mixture into the furnace combustion chamber;

i. a closure disc which is mounted on the front end of the slidablepilot tube, which has a central opening therein that joins into thefront end of the pilot tube, which can move backward with the slidablepilot tube to seat into and close the front end opening in the mixingchamber, and which can move forward with the slidable pilot tube todisengage from the front end opening in the mixing chamber;

j. a pilot fitting connected into the rear end of the pilot tube,including an inlet conduit therein for conducting a fuel gas-air mixtureinto said pilot fitting;

k. an ignitor fitting which is connected into the pilot fitting, whichhas a fuel gas inlet conduit therein for conducting a fuel gas into theignitor fitting, which has an air inlet conduit therein for conductingair into said ignitor fitting, and which includes a means mounted in theignitor fitting for igniting the fuel gas-air mixture directed into saidfitting;

1. an ignitor tube which has an open front end and an open rear end,which extends centrally through the pilot fitting and the pilot tube,with the rear end being connected into the ignitor fitting and the frontend being flush with the front end of the opening in the closure disc,and which is adapted to carry the ignited fuel mixture from the ignitorfitting into the furnace combustion chamber.

2. The burner assembly of claim 1 including an air operator unit whichis operatively connected into the air inlet conduit in the mixingchamber and into the pilot tube, the said air unit providing means forautomatically moving the pilot tube and closure disc backward or forwardin response to air pressure fluctuation in the front compartment of themixing chamber.

3. The burner unit of claim 1 which includes a temperature sensorconnected into the pilot fitting, the sensor providing means fordetecting a temperature change in the ignited fuel mixture in theignitor tube.

1. A burner unit for use with a furnace for burning combustible gases, which includes: a. a fuel gas mixing chamber having an open front end and a closed rear end, the burner unit being adapted for mounting on a furnace with the open front end of the mixing chamber in communication with the combustion chamber of the furnace; b. a tube sheet positioned crosswise in the mixing chamber and spaced from each end of the chamber; c. a rear compartment in the mixing chamber defined by the space between the tube sheet and the rear end of the chamber; d. a front compartment in the mixing chamber defined by the space between the tube sheet and the front end of the chamber; e. a tube bundle comprising several open end tubes in spaced apart, parallel relation, each tube being connected at one end into the tube sheet, such that one open end of each tube communicates with the rear compartment of the mixing chamber and the opposite open end of each tube communicates with the front compartment of said mixing chamber; f. a fuel gas inlet conduit connected into the rear compartment of the mixing chamber, which is adapted for conducting a fuel gas into said rear compartment; g. an air inlet conduit connected into the front compartment of the mixing chamber, which is adapted for conducting air into said front compartment; h. a pilot tube which has an open front end and an open rear end, which is slidably mounted on the tube sheet and the rear end of the mixing chamber, which extends centrally through the rear compartment and the front compartment of the mixing chamber, and which is adapted for conducting a fuel gas-air mixture into the furnace combustion chamber; i. a closure disc which is mounted on the front end of the slidable pilot tube, which has a central opening therein that joins into the front end of the pilot tube, which can move backward with the slidable pilot tube to seat into and close the front end opening in the mixing chamber, and which can move forward with the slidable pilot tube to disengage from the front end opening in the mixing chamber; j. a pilot fitting connected into the rear end of the pilot tube, including an inlet conduit therein for conducting a fuel gas-air mixture into said pilot fitting; k. an ignitor fitting which is connected into the pilot fitting, which has a fuel gas inlet conduit therein for conducting a fuel gas into the ignitor fitting, which has an air inlet conduit therein for conducting air into said ignitor fitting, and which includes a means mounted in the ignitor fitting for igniting the fuel gas-air mixture directed into said fitting; l. an ignitor tube which has an open front end and an open rear end, which extends centrally through the pilot fitting and the pilot tube, with the rear end being connected into the ignitor fitting and the front end being flush with the front end of the opening in the closure disc, and which is adapted to carry the ignited fuel mixture from the ignitor fitting into the furnace combustion chamber.
 2. The burner assembly of claim 1 including an air operator unit which is operatively connected into the air inlet conduit in the mixing chamber and into the pilot tube, the said air unit providing means for automatically moving the pilot tube and closure disc backward or forward in response to air pressure fluctuation in the front compartment of the mixing chamber.
 3. The burner unit of claim 1 which includes a temperature sensor connected into the pilot fitting, the sensor providing means for detecting a temperature chanGe in the ignited fuel mixture in the ignitor tube. 